Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a first image in a sequence for a first embodiment of a display screen or portion thereof with transitional graphical user interface, showing our new design;

FIG. 2 is a front view of a second image thereof; and,

FIG. 3 is a front view of a third image thereof.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-3 and FIGS. 4-6. The process or period in which one image transitions to another image forms no part of the claimed design.

The outer perimeters illustrated by a pair of broken lines depict a display screen or a portion thereof and form no part of the claimed design. The remaining broken lines shown in the drawings depict portions of the transitional graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 